1. Field of the Invention
The present invention is in the field of heart valve prostheses. More particularly, the present invention is directed to an improved hinge mechanism for mechanical heart valve prostheses of the type having two valve leaflets which move in a limited pivoting motion to regulate the blood flow through the valve prostheses.
2. Brief Description of the Prior Art
Heart valve prostheses are well known in the art. Generally speaking, heart valve prostheses can be classified in two major types or categories. More particularly, one type of prostheses employs a tissue valve of animal (usually porcine) origin in its blood flow regulating valve mechanism. The other type of heart valve prosthesis utilizes a ball, a disc, valve leaflets or other mechanical valving devices to regulate the direction of blood flow through the prosthesis. The latter type of prosthesis is usually known in the art as "mechanical" heart valve prosthesis. For specific examples and detailed descriptions of the heart valve prostheses of the prior art, reference is made to U.S. Pat. Nos. 3,744,062; 3,835,475; 3,997,923; 4,364,126 and 4,106,129.
By their very nature, the mechanical heart valve prostheses have metal or plastic surfaces which, when exposed to the blood flow, are usually thrombogenic long after implantation of the prosthesis through open heart surgery. One of the problems the prior art heart valve prostheses have strived, but not fully succeeded to solve, relates to minimizing the thrombogenic effects created by the exposed metal or plastic surfaces.
Other problems which, generally speaking, all heart valve prostheses of the prior art have strived, but not fully succeeded to solve, relate to the ease of implantability, and reliability of operation of the valves. In this regard it will be readily appreciated by those skilled in the art that structural failure of an implanted artificial heart valve is likely to be fatal for the bearer of the heart valve. With regard to the ease of implantability of the artificial heart valves, it will be readily appreciated that open heart surgery presents difficult conditions. In order to minimize risk to the patient, the heart valve prostheses must be capable of being assembled and mounted in place in as few and simple steps as possible.
U.S. Pat. No. 4,276,658 discloses a "mechanical type" heart valve prosthesis which is designed to reduce the problem of thrombogenecity caused primarily by exposed metal or plastic surfaces of the valve. More specifically, it is known in this regard that thrombogenecity is caused not only by exposed metal or plastic surfaces, but also by areas or cavities disposed in an artificial heart valve which permit stagnation of blood flow and therefore permit the formation of incipient blood clots. Such areas of stagnated blood flow, or surfaces which are not continuously cleansed or wiped, are, therefore, undesirable and dangerous in the mechanical heart valve prostheses.
The artificial heart valve of U.S. Pat. No. 4,276,658 attempts to minimize the foregoing problem by providing surfaces coated with pyrolytic carbon, which is known to virtually lack thrombogenecity. Moreover, the mechanical heart valve of the above-noted patent employs two valve leaflets, each of which has an arcuate protrusion retained in matching depressions located in ears formed integrally with the annular base of the valve. An advantage of the mechanical heart valve of this patent is said to lie in the continuous "cleansing" or "wiping" action exerted by the moving arcuate portions, which help to remove any incipient blood clots from the depressions formed in the ears. However, the depressions, which must be kept free of blood clots, are relatively remotely disposed from the main stream of blood flow.
In light of the foregoing there is a need in the prior art for further improvements in mechanical heart valve prostheses with regard to simplicity and cost of construction, reliability of operation, and reduction of thrombogenecity. The mechanical heart valve of the present invention provides such an improvements.